This invention relates generally to a filtration system using ultrasound devices for selectively removing particulate from filter media.
The basic process of filtration is the separation of solids and liquids. Various filtration techniques have been tried in the past, but clogging of filters, can be a problem particularly in industrial applications where flow rates are important for process and production rates. Flow rates can diminish upon clogging of the filter through which the fluid passes. Cross-flow filtration may improve filtration performance in certain applications. Such filtration has already found applications in the dairy industries, fruit and beverage production industries, water purification processes, and in pharmaceutical and biotechnology industries.
Filtration can be substantially enhanced by using ultrasound as noted in Ultrasound: Its Chemical, Physical and Biological Effects, edited by S. Suslick, 1988. Impact of ultrasound slows the cake buildup, increases flow rates, reduces barrier cleaning frequency, and delivers drier solids. These experiments used metallic and sandstone barriers with pore sizes from a few microns to over 100 microns. Using a 20 kHz ultrasound frequency, the investigators treated contaminated oil and coal slurries.
Ultrasound is a mechanical form of energy with frequencies above 18 kHz. It can impact solids, liquids, and gasses under appropriate conditions causing either temporary or permanent physical and chemical changes. Sonar systems in ultrasound range have been known since World War I.
Since the 1950s, ultrasound has been well recognized in cleaning applications. The basis for this is the ability of ultrasound to vibrate its target to loosen dirt and solids away from the contact surface. Ultrasound applications today abound in medical diagnostics, process control, soldering, and numerous mechanical biological and chemical areas.
High frequency (500 kHz) ultrasound has been used to bombard aqueous and organic suspensions. This breaks the molecules and generates chemically active radicals which then react with other radicals and molecules. There is a potential to apply ultrasound for toxic chemicals destruction.
In applications where fluids pass through a filtering medium situated substantially perpendicular to the flow of the fluid, the normal filtration process is slowed when the solids it separates from a fluid flow accumulate on the filter media, eventually clogging the filter altogether such that fluid flow therethrough is greatly diminished or altogether prevented. Techniques have been developed which vibrate the filter media for cleaning, and also flow pulsing/reversing techniques have been used which also clean the filter media. Polymers and chemicals have been used to reduce caking of solids on the filter media, and additionally, filter-aids like coagulant additives have been used to increase flow rates.
A problem with flow-through filtration is that typical filter media becomes clogged and requires manual cleaning. Often times this cleaning presents a danger to personnel if the waste stream contains any harmful components. Backwashing, flow pulsing, and filter media vibrations have shown some promise in effectively removing caked-on solids on the filter media, and are available commercially. However, these techniques can involve complicated equipment and may be cost prohibitive. Pressure and vacuum filtration techniques may present similar problems.
While the foregoing systems are known, there still exists a need for apparatus and methods for improving the efficiency of separating solid matter from filter media, and in particular, to perform such separation using automated devices and methods.